When manufacturing molded articles by injection molding machines, a large number of molding conditions such as mold clamping force, injection speed, hold pressure, hold time, resin temperature, mold temperature, back pressure, screw rotating speed, suckback amount, cooling time, etc. must be determined. Therefore, in general, injection molding is first carried out by way of trial under the molding conditions which are tentatively determined on the basis of expert knowledge and experience in accordance with the type of article to be molded. Thereafter, one or more molding conditions are modified in accordance with the expert knowledge and experience, depending on the type of molding defect appearing in the resultant molded article, such as flash, sink mark, warp, weld mark, flaw mark, etc., and then injection molding is tried again. This molding condition determination process is repeatedly executed to find optimum molding conditions that do not cause any molding defect. Accordingly, the determination of optimum molding conditions involves considerable labor. In particular, when producing various molded articles of different types by using a plurality of injection molding machines having different structures from one another, the molding condition determining process must be performed for each of the injection molding machines, requiring much labor to determine the optimum molding conditions.